This chapter is from the book

There's a classic Saturday Night Live commercial parody for a product called Shimmer, in which a husband (played by Dan Aykroyd) and wife (Gilda Radner) argue over whether the product is a floor wax or a dessert topping. As the debate escalates, a slick pitchman (Chevy Chase) breaks it up by stating that Shimmer is both a floor wax and a dessert topping.

Illustrator is a lot like Shimmer because it serves so many disparate needs. It's a print-based application that's also a Web graphics creation tool with a pixel grid. It's a vector-based object-creation model that supports transparency and Photoshop-like effects, and now creates naturalistic brush strokes. It's a two-dimensional tool that has rudimentary three-dimensional modeling and now allows you to draw in perspective.

Whatever task you throw at Illustrator, or whatever your particular artwork needs are, there are a multitude of features that help you explore creatively, work efficiently, and publish reliably.

#25 Understanding the Perspective Grid

Illustrator's new Perspective Drawing feature gives artists the ability to define a perspective grid, draw art on that grid, and add existing art to that grid in the appropriate perspective. This speeds up perspective-based drawing, but before you start drawing you need to understand the grid you're drawing on and its various settings and controls.

Every Illustrator document contains one perspective grid. By default, that grid is not shown. To reveal a document's perspective grid, go to View > Perspective Grid > Show Grid, or press Shift-Command-I (Shift-Ctrl-I). The default is a two-point perspective grid, but Illustrator has built-in grid presets for one-, two-, and three-point perspective drawing (Figure 25a) that you can also use as the basis for your drawing.

To understand perspective, think about where the viewer is in physical space.

One-point perspective is what the viewer would see standing in the center of a long hallway, looking straight ahead. All planes (walls, ceiling, floor, etc.) converge to a single point—known as the vanishing point—on the horizon. The horizon line is always at eye level.

Two-point perspective is what the viewer would see standing in the center of a four-way intersection, looking directly at the corner of one block. To the left, the buildings down one street recede in one direction. To the right, the buildings recede in another direction toward a second vanishing point. Both points share the same horizon line.

Three-point perspective is what you'd see flying in a helicopter looking down at that intersection. Buildings still recede off into the distance toward two vanishing points and one horizon line, but all the buildings' lines (from the rooftop to the street) also converge downward toward a third vanishing point.

You can make the grid visible simply by switching to the Perspective Grid tool (Shift-P). This tool makes all of the grid's modification points active so you can reposition its horizon line or left and right planes, extend or redistribute its grid lines, and otherwise customize it to your needs. Any grid you customize can be saved as a preset to use in any other Illustrator document (View > Perspective Grid > Save Grid as Preset).

Customizing the Perspective Grid

Illustrator's perspective grid projects forward, so adjusting a grid to match a scanned sketch is pretty simple if the sketch's composition matches that default. However, not all perspective drawings are composed that way. The sketch in Figure 25b, for example, recedes toward its center.

Although the grid you see in your document appears to occupy a finite area defined by the grid lines for each plane, the perspective grid is, in fact, everywhere in the document. Moving objects in perspective beyond the visible edges of the grid doesn't remove them from its control. Instead, those objects appear farther above or below the grid's horizontal boundaries, or nearer to or farther back from its vertical boundaries, and they remain drawn in proper perspective.

Fortunately, grids can be customized. When the Perspective Grid tool is active, each grid plane has a control handle with which you can reposition that grid. If we move the handle for the right plane to the left, for example, the right grid plane can act as the grid for the left wall in the sketch (Figure 25c).

Figure 25c The right grid plane is moved to the left using its control handle (inset) to a position that matches the left wall of the sketch.

Common Ground

Regardless of the type of perspective grid you choose, all grids share these basic components:

a horizon line

a left plane (two- and three-point perspective grids also contain a right plane)

a ground plane

Station Point=Pivot Point

The station point of a two- or three-point perspective grid is the front-most corner of the cube formed by the grid. When you lock a grid's station point (View > Perspective Grid > Lock Station Point), your changes to the grid's vanishing points are inversely mirrored. In other words, moving the left plane's vanishing point inward moves the right plane's vanishing point outward by an equal amount, and vice versa. With the station point locked, the two planes effectively pivot from the point where they meet as you move either vanishing point.

Once the grid plane is placed in the approximate position, its vanishing point can be moved to get the perspective angle as close to the sketch as possible (Figure 25d). With the plane positions transposed, their respective extents will overlap and create a very busy grid. This can be prevented by dragging the hollow diamond shapes (which control the grid extents) on the repositioned plane in toward where the two walls meet (Figure 25e).

Figure 25d Moving the vanishing point (inset) sets an angle that better matches the original sketch.

Figure 25e Pulling in the grid extents diamonds (inset) displays fewer grid lines and prevents the two grids from overlapping.

Tone Down Your Grid

As you add artwork, the perspective grid can become distracting. To minimize this, open the Define Perspective Grid dialog box (View > Perspective Grid > Define Grid) and change the grid's opacity from the default of 50 percent to something easier on the eyes, like 25 percent. Unfortunately, there's no application-wide way to change the default.

Similar position, vanishing point, and grid extent adjustments can be made to the left plane so that it can serve as the grid for the right wall in the sketch. Once that's done, the grid is completely customized for the perspective needs of this illustration (Figure 25f). Once the grid is established, the next step is mastering the appropriate drawing strategies to produce a finished perspective illustration (Figure 25g).

Figure 25f The customized perspective grid with its planes repositioned, horizon line adjusted, and grid extents pulled in to match the sketch.

Figure 25g A finished perspective drawing from the original sketch and the customized grid.

Grid Goodies, Part 1

When Illustrator's Smart Guides feature is turned on (which is the default) and you reposition the grid's horizon line, an "HH" value is displayed. This number indicates the horizon height, which is the distance between the horizon line and the ground line. If you're working on a drawing to scale, it can be helpful to put the grid's horizon line at a normal observer's height.

Grid Goodies, Part 2

The Define Perspective Grid dialog box (View > Perspective Grid > Define Grid) is your go-to place for all the perspective settings. From here, you can choose what type of grid to use (one-, two-, or three-point perspective), and select its measurement system, scale, gridline increments, viewing angle, horizon height, and the color of the left, right, and horizontal planes.